Just do make sure that, if you have a W207/W212 you have the later version of the system that can be configured for the higher resolution display in the W207/W212.
We forgot this once, and so have a new (but installed and straight away removed) Nav 20 in the office, and look for someone with a NTG4 Audio-20 that may want it installed !!
I seem to recall that the earlier (w204 only) system had the connector port clip into the car's light, whereas newer one had a small oblong set of connectors. The early one if i'm not mistaken supports Bluetooth audio streaming too, the later does not. The earlier one gets the same NAV20 software update stick as the later one.
R